Characterization of Extracted Lignin of Bamboo (neosinocalamus Affinis) Pretreated with Sodium Hydroxide/urea Solution at Low Temperature

Ball-milled bamboo (Neosinocalamus affinis) was first treated under ultrasound at 20 C in 95% ethanol solution for 0 to 50 min, dissolved in sodium hydroxide/urea solution (7% NaOH/12% urea) at –12 C, and then extracted with ethanol and dioxane to isolate lignin. The structure of the isolated lignin was characterized with a set of wet chemical and spectroscopic methods, including UV, FT-IR, C NMR, and HSQC spectroscopies. The results showed that the lignin extracted from bamboo consisted of p-hydroxyphenyl (H), guaiacyl (G), and syringyl (S) type lignins with minor cinnamate units. The predominate lignin interunits were β-O-4 ́ ether linkages, followed by phenylcoumaran and a lower proportion of resinol and spirodienone. It was also found that the ester groups of lignin were cleaved during the pretreatment process with cold alkaline solution.